Multicolor, multilayer photographic elements are well known in the art of color photography. Usually, these photographic elements have three different selectively sensitized silver halide emulsion layers coated on one side of a single support. The vehicle used for these emulsion layers is normally a hydrophilic colloid, such as gelatin. One emulsion layer is blue-sensitive, another green-sensitive and another red-sensitive. Although these layers can be arranged on a support in any order, they are most commonly arranged with the support coated in succession with the red-sensitized layer, the green-sensitized layer and the blue-sensitized layer (advantageously with a bleachable blue light-absorbing filter layer between the blue-sensitive layer and the green-sensitive layer) or with the opposite arrangement and no filter layer. Colored photographic images are formed from latent images in the silver halide emulsion layers during color development by the coupling of oxidized aromatic primary amine color developing agent with couplers present either in the color developer solution or incorporated in the appropriate light-sensitive layers. Color photographic elements containing dye images usually utilize a phenolic or naphtholic coupler that forms a cyan dye in the red-sensitized emulsion layer, a pyrazolone or cyanoacetyl derivative coupler that forms a magenta dye in the green-sensitized emulsion layer and an acetylamide coupler that forms a yellow dye in the blue-sensitive emulsion layer. Diffusible couplers are used in color developer solutions. Nondiffusing couplers are incorporated in photographic emulsion layers. When the dye image formed is to be used in situ, couplers are selected which form non-diffusing dyes. For image transfer color processes, couplers are used which will produce diffusible dyes capable of being mordanted or fixed in the receiving sheet.
In the production of color photographic images, it is necessary to remove the silver image which is formed coincident with the dye image. This can be done by oxidizing the silver by means of a suitable oxidizing agent, commonly referred to as a bleaching agent, in the presence of halide ion; followed by dissolving the silver halide so formed in a silver halide solvent, commonly referred to as a fixing agent. Alternatively, the bleaching agent and fixing agent can be combined in a bleach-fixing solution and the silver removed in one step by use of such solution.
A commercially important process intended for use with color reversal photographic elements which contain the couplers in the silver halide emulsion layers, or in layers contiguous thereto, utilizes, in order, the following processing baths: first developer, wash, reversal bath, color developer, bleach, fix, wash and stabilizer. In this process, the first developer reduces the exposed silver halide to metallic silver; the reversal bath nucleates the silver halide that remains after first development, the color developer converts the nucleated silver halide to metallic silver and forms the dye images, the bleach converts all metallic silver to silver halide, the fix converts the silver halide into soluble silver complexes that are washed from the element, and the stabilizing bath improves image dye stability.
In one particularly advantageous form of the aforesaid color reversal process, a bleach-accelerating bath is employed between the color developing bath and the bleaching bath. Such a bleach-accelerating bath is also referred to in the photographic field as a "conditioning bath". It is used to "condition" the metallic silver, developed in the first and color developers, for complete oxidation to silver halide and to help preserve the acidity of the bleach solution by reducing carryover of color developer into the bleach. The conditioning bath contains, as an essential ingredient, an effective amount of a bleach-accelerating agent. This agent is imbibed into the emulsion layers of the photographic element during treatment with the conditioning bath and, accordingly, is present to exert its beneficial influence in situ when the photographic element enters the subsequent bleach bath.
A wide variety of effective bleach-accelerating agents are well known in the art of photographic color processing. Examples of particularly effective bleach-accelerating agents include aliphatic thiols, heretocyclic thiols, disulfides, thioethers, and persulfates. References describing specific agents which exhibit very effective bleach-accelerating capabilities include British Patent No. 1,138,842 published Jan. 1, 1969 and U.S. Pat. No. 3,893,858 issued July 8, 1975.
It is well known in the photographic art to utilize a stabilizing bath as the final step in the processing of both color films and color papers. Such baths can serve to reduce stain and/or enhance dye stability. A wide variety of different stabilizing compositions have been proposed for such use. Thus, the known stabilizing baths include those containing thiourea or a substituted thiourea as described in Kellog, U.S. Pat. No. 2,487,446 issued Nov. 8, 1949; aliphatic aldehydes as described in Harsh et al, U.S. Pat. No. 2,518,686 issued Aug. 15, 1950; addition products of formaldehyde and a urea, as described in Mackey, U.S. Pat. No. 2,579,435 issued Dec. 18, 1951; tetramethylol cyclic alcohols or ketones as described in Clarke et al, U.S. Pat. No. 2,983,607 issued May 9, 1961; glucoheptonates as described in Bard, U.S. Pat. No. 3,157,504 issued Nov. 17, 1964; carbohydrazides as described in Larson, U.S. Pat. No. 3,201,244, issued Aug. 17, 1965; amino acids as described in Jeffreys, U.S. Pat. No. 3,291,606 issued Dec. 13, 1966; mixtures of an aldehyde and an alkoxy-substituted polyoxyethylene compound as described in Seemann et al, U.S. Pat. No. 3,369,896 issued Feb. 20, 1968; compounds comprising a tri(hydroxymethyl)methyl group as described in Jeffreys et al, U.S. Pat. No. 3,473,929 issued Oct. 21, 1969; and addition complexes of an alkali metal bisulfite and an aldehyde as described in Mowrey, U.S. Pat. No. 3,676,136 issued July 11, 1972. The use of more than one active agent in such stabilizing baths is also known. For example, U.S. Pat. No. 3,676,136 to Mowrey describes the use of antioxidants such as glucose, galactose, sorbitol or mannitol in a stabilizing bath in addition to an aldehyde bisulfite addition complex.
Magenta dye stability is a particularly serious problem in color photography, as the magenta dye image tends to fade much more rapidly than either the cyan dye image or the yellow dye image. The dark-keeping stability of magenta image dyes derived from pyrazolone couplers is adversely affected by the presence of the coupler itself. This is particularly evident in the toe and midscale regions of the green sensitometric curve. In these areas, there is a substantial amount of the unreacted coupler. This unreacted coupler undergoes complex chemical reactions with the magenta dye.
For many years, formaldehyde has been commonly used as a stabilizing agent in photographic color processing to provide enhanced magenta dye stability. The photographic element is treated with a final bath--called a "stabilizing bath"--that contains formaldehyde. The formaldehyde reacts with the unused coupler in the film, forming a stable compound that will not react with the magenta dye. Under normal processing conditions, this reaction is completed in the drying oven. However, while formaldehyde is a very effective stabilizing agent for this purpose, its use is highly disadvantageous from an ecological standpoint because of the well known ecological concerns relating to formaldehyde.
It is toward the objective of providing an improved bleach-accelerating composition which does an effective job of accelerating the bleaching action of the subsequently utilized bleaching agent, and which provides improved dye stability so as to eliminate the need for a stabilizing bath, that the present invention is directed.